It has been known that polymers of .epsilon.-caprolactone can be readily prepared via reactions of the .epsilon.-caprolactone monomer with a hydroxyl or amine initiator which can lead to a hydroxyl terminated polymer, as shown by the equation: ##STR1##
Similar types of reactions can lead to a variety of different molecular weight polymers; however generally the most desirable polymers have number average molecular weights as measured by GPC of about 1000 to about 5000. The above synthesis is a very desirable one because the functionality is preserved extremely well, and one achieves in the product essentially all the hydroxyl groups that are added prior to the polymerization.
The use of caprolactone as a polymerizing monomer to obtain very high molecular weight polymers is also well-known. In these cases, molecular weights on the order of 50 to 100,000, are readily obtained by the use of certain types of catalysts. In those polymerizations, initiators are normally not employed or employed at very low levels. Typically, in any of these two aforementioned polymerization processes, the degree of polymerization is determined by the amount of initiator employed as follows: ##EQU1##
The polymerization of these lactone monomers including .epsilon.-lactone yields a hydroxyl terminated polymer. These aforementioned processes do not teach one how to obtain a polymer which is terminated, at least at one end, by an amine group. For example, if an amine such as a primary amine, n-butyl amine, is utilized to initiate .epsilon.-caprolactone polymerization, a product is obtained which has a hydroxyl group on one end and an amide group on the other. In other words, the reaction always leads to a propagating species which is hydroxyl terminated. If one employs a diamine, essentially the same situation ensues, that is, one gets a propagating species which has a hydroxyl group on each end of the polymer chain. This is desirable for many applications, but it does limit the utility of the caprolactone technology primarily to hydroxyl functionality.
The instant invention describes a process which permits the preparation of a new class of polylactones derived from lactone monomers. The process, as described herein, involves the use of amine containing initiators which are amine-containing heterocyclic structures with at least 2 amine groups, where at least one nitrogen atom is contained in a heterocyclic ring as a tertiary amine and a second (or more) nitrogen atom is attached to the ring, and is a primary or secondary amine. The resulting polymeric products have tertiary amine-containing heterocyclic ring at one end as shown in the following equation: ##STR2## wherein n=1 to 500; m=0 to 20. Other initiators are also contemplated in this invention. The exact position where the primary amine terminated-aliphatic chain is attached to the heterocyclic ring is not important; the structures above are representative.